Without first seeing your data or the chart you want, take note of what the standard deviation error bars are. Look at SGIII's post and the chart he attached. All the error bars are the same. They are the standard deviation of the entire data set (the series he charted). If I understand what you are trying to chart, you have multiple (three) Y's for each X and want the standard deviation for each X. I am assuming you are plotting all three Y points for each X as separate series. You will need a column in your table for the average and the stdev for each set of three points. You plot the average as another series (then immediately make it the top series by changing it's "order" to 1) and choose your stdev column for the custom error bars. I changed the data symbol to a + and added connection lines, too. The base chart is a scatter chart in the screenshot below.
If I am off the mark, no problem, just ignore me. I know you said you had "stress measure for the before and after of 3 repeats of my experimental condition" which might really just be a chart of three points vs the chart I did.
